Fertilizing Desert Garden Roses

Don't guess at what the plant needs. Get expert advice.

Jul 3, 2006

With roses, it's better not to guess whether yellowing leaves are caused by a mineral deficiency or by a virus.

There are many diseases and deficiencies that can affect roses in desert gardens, so it's better not to guess about them.

Although iron chlorosis causes leaves to turn yellow, certain viruses can also do the same thing. However, viruses will usually yellow the leaves in spots. And every mineral deficiency exhibits its own symptoms.

For instance, roses need lots of nitrogen. Bush roses bloom on new growth. And that new growth is cyclical. Since nitrogen is chiefly responsible for this cyclical growth, it stands to reason that nitrogen is one of the plant's main nutrients.

The cycle develops by the plant sending up vigorous shoots. This is followed by formation of flower buds. This process is repeated throughout the blooming season.

Nitrogen deficiency will affect the stems and shoots, causing them to be short and weakened, and much less vigorous. Those shoots will also bring forth smaller and faded-looking flowers, if they flower at all. Nitrogen deficiency will also cause the leaves to turn a yellowish-green.

In order to keep your roses vigorous and full-blooming throughout the season, apply nitrogen, beginning just before the buds begin to break in early spring.

To keep nitrogen level at the level needed, apply ammonium sulfate. Two tablespoons per plant every four to six weeks until about three weeks before the first fall frost should suffice. (You can increase or decrease the amount by watching the growth of the plant.)

Deficiency in phosphorous may make older leaves drop, without them turning yellow first. It will also weaken the stems and slow bud development. Phosphorous is necessary to develop flower buds. Apply phosphorous when you apply nitrogen. One fifth to one-fourth cup of 10-10-0, 10-20-0 or 16-20-0 fertilizer worked into the soil evenly underneath the rose canopy will provide enough nutrients for the plant to get off to a good start in early spring. Make the same application when the new growth of the plant is about six inches long. Apply a third time when the first blossoms have faded. Then you should stop applying until next spring.

Iron deficiency was mentioned in another article, but we'll touch on it again here. Iron deficiency is pretty common in desert gardens. The first indication of iron deficiency is light yellowing in the tips of young leaves. In time, the yellowing progresses until all the area between the veins become yellow, while the larger veins stay dark green. You can bring iron deficiency under control by applying iron chelates (from the Greek chelas = claw) to the soil. Because lime and other alkaloids in desert soils prevent the plant roots from taking in iron from the soil, these specialized chelates should be used. The iron chelate molecules bond to water molecules, allowing the roots to take in iron.

Next article: Pests and diseases that might infect the roses in your desert garden.